Methods and apparatus to minimize the effect of tape tension in electronic device polishing

ABSTRACT

Methods and apparatus are provided for reducing tension on a polishing roller. In some aspects, a polishing head may be provided that is adapted to contact a substrate. The polishing head includes: a polishing unit having a polisher and at least one pair of tension distributors adapted to reduce tension on the polisher; and one or more pairs feed guides. Numerous other aspects are provided.

The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/108,102, filed Oct. 24, 2008, and entitled “METHODS AND APPARATUS TO MINIMIZE THE EFFECT OF TAPE TENSION IN ELECTRONIC DEVICE POLISHING” (Attorney Docket No. 12834/L), which is hereby incorporated herein by reference in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to electronic device manufacturing, and more specifically to methods and apparatus for minimizing the effect of tape tension in electronic device polishing.

BACKGROUND OF THE INVENTION

Substrates are used in electronic device manufacturing. During processing, a film may be deposited on the surface of a substrate. However, it may be undesirable to have a film on the edge of the substrate, as it may negatively affect the electronic devices formed on the substrate. Accordingly, methods and apparatus for efficiently and effectively removing a film from the edge of the substrate are desirable.

SUMMARY OF THE INVENTION

In some aspects of the invention, an apparatus is provided that includes a polishing head, adapted to contact a substrate. The polishing head includes: (1) a polishing unit having a polishing roller and at least one pair of tension rollers adapted to reduce tension on the polishing roller; and (2) one or more pairs of stationary feed rollers.

In other aspects of the invention, a system is provided that includes a substrate support adapted to rotate a substrate; and a polishing head, adapted to contact a substrate. The polishing head includes (1) a polishing unit having a polishing roller and at least one pair of tension rollers adapted to reduce tension on the polishing roller, and (2) one or more pairs of stationary feed rollers. The system also includes a controller adapted to operate the polishing head.

In yet other aspects of the invention, a method is provided that includes (1) rotating a substrate; (2) selecting a balanced position for a polishing head; (3) contacting the substrate with a polishing film, whereby the polishing film is routed through the polishing head; (4) applying a force to the substrate via the polishing film; and (5) pivoting the polishing head about the substrate.

Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an embodiment of a system for polishing parts of a substrate in accordance with the present invention.

FIG. 2 is a schematic perspective view of an embodiment of a polishing apparatus for polishing a substrate in accordance with the present invention.

FIG. 3A is a plan view of an exemplary polishing head.

FIG. 3B is a schematic plan view of a portion of the exemplary polishing head shown in FIG. 3A.

FIG. 4A is a perspective view of a polishing head in accordance with the present invention.

FIG. 4B is a schematic plan view of a portion of the polishing head shown in FIG. 4A in accordance with the present invention

FIG. 5 is a close-up schematic plan view of the polishing head shown in FIG. 4A in accordance with the present invention.

FIG. 6 is a pictorial flow diagram providing an exemplary recipe in accordance with the present invention.

FIG. 7 is a flowchart providing an exemplary method in accordance with the present invention.

DETAILED DESCRIPTION

Substrates used in semiconductor processing often have films and/or surface defects, which typically should be removed prior to subsequent processing steps. In some cases, these films and defects may occur on the edge of a substrate, including notches formed thereon. In conventional systems, the films and/or defects may be removed via a polishing apparatus that may include an abrasive polishing tape and/or abrasive pad adapted to contact and polish the edge and/or notch of the substrate.

The polishing tape typically is routed from a supply spool, over at least one feed guide, to a take-up spool. The rotation of the take-up spool may cause the polishing tape to advance from the supply spool. As the substrate rotates, a polisher may press the advancing polishing tape against the substrate. The polisher may exert a force, often a downward force, on the polishing tape as the polisher presses the polishing tape against the substrate, and the polishing tape, which is tensioned between the supply and take-up spools, may exert an opposing force or “tape tension” on the polisher. Therefore, the tape tension should be taken into account when determining the amount of force used to press the polisher against the substrate (via the polishing tape). However, the tape tension may vary based on, for example, the position of the polisher, the amount of polishing tape on either of the take-up or supply spools, etc. Other parameters may cause the tape tension to vary.

In some embodiments of the present invention, the tape tension may be reduced with an inventive polishing head design. The inventive polishing head design may include a polishing unit having the polisher and two additional guides (hereinafter referred to as “tension rollers”), which may be oriented to allow the polishing tape to lay substantially flat between feed guides and the polisher. Because the polishing tape lays substantially flat, the tape tension may be distributed differently, compared to other exemplary apparatuses, as described below, and therefore may apply less force on the polishing unit.

Additionally, in some embodiments of the present invention, the tension rollers may be coupled to the polishing head such that the polishing tape may be routed through the polishing head without removing the feed guides.

FIG. 1 is a schematic plan view of an exemplary embodiment of a system 100 for polishing a portion of a substrate 102, such as a substrate edge 104 and/or a substrate notch (not shown). The system 100 of FIG. 1 includes three polishing apparatuses 108, each including a polishing head 110. However, any number and type of apparatus 108/heads 110 may be used in any practicable combination. In addition, in such multi-head embodiments, each head 110 may use a differently configured or type of a polishing tape (e.g., different grits, materials, tensions, pressures, etc.) to contact and polish the substrate edge 104 and/or notch. Any number of heads 110 may be used concurrently, individually, and/or in any sequence. The heads 110 may be disposed in different positions and/or in different orientations (e.g., aligned with the substrate edge 104 and/or notch, normal to the substrate edge 104 and/or notch, angled relative to the substrate edge 104 and/or notch, etc.) to allow polishing tape, pushed by a roller or pad in some embodiments (FIG. 2), to polish different portions of the substrate edge 104 and/or notch.

In some embodiments, one or more of the heads 110 may be adapted to be oscillated or moved (e.g., pivoted or angularly translated about a tangential axis of the substrate 102 and/or circumferentially relative to the substrate 102) around or along the substrate edge 104 and/or notch so as to polish different portions of the substrate edge 104 and/or notch. In some embodiments, one or more of the heads 110 may be adapted to continuously or intermittently oscillate between the various positions. Alternatively, one or more of the heads 110 may be fixed and/or only adjusted while the substrate 102 is not being rotated. In yet other embodiments, the substrate 102 may be held fixed while one or more of the heads 110 oscillate (as described above) as well as rotate circumferentially around the substrate 102. This movement may be under the direction of a programmed or user operated controller 112, described below. Different heads 110 may be used for different substrates 102 or different types of substrates 102.

As described above, the system 100 may further include the controller 112, (e.g., a programmed computer, a programmed processor, a microcontroller, a gate array, a logic circuit, an embedded real time processor, etc.), which may control the driver(s) used to rotate the substrate 102 and/or the actuator(s) used to push a polisher (FIG. 2) against the substrate edge 104 and/or notch. Note that the controller 112 may be coupled (e.g., electrically, mechanically, pneumatically, hydraulically, etc.) to each of a plurality of actuators. Likewise, the controller 112 may be adapted to receive feedback signals from one or more drivers and/or actuators, that indicate the amount of energy being exerted to rotate the substrate 102 (e.g., rotate a vacuum chuck holding the substrate 102) and/or actuate the actuator(s) to push the polisher against the substrate 102. These feedback signals may be employed to determine when a particular layer of film has been removed from the edge 104 and/or notch of the substrate 102 and/or whether a sufficient amount of substrate polishing has occurred.

As mentioned above, substrate polishing may be performed using one or more polishing apparatuses 108. In one or more embodiments, a plurality of polishing apparatuses 108 may be employed, in which each polishing apparatus 108 may have similar or different characteristics and/or mechanisms. In the latter case, particular polishing apparatuses 108 may be employed for specific operations. For example, one or more polishing apparatuses 108 may be adapted to perform relatively rough polishing and/or adjustments while another one or more polishing apparatus 108 may be adapted to perform relatively fine polishing and/or adjustments. Polishing apparatuses 108 may be used in sequence so that, for example, a rough polishing procedure may be performed initially and a fine polishing procedure may be employed subsequently as needed or according to a polishing recipe. The plurality of polishing apparatuses 108 may be located in a single chamber or module, as shown herein, or alternatively, one or more polishing apparatuses 108 may be located in separate chambers or modules. Where multiple chambers are employed, a robot or another type of transfer mechanism may be employed to move substrates between the chambers so that polishing apparatuses 108 in the separate chambers may be used in series or otherwise.

FIG. 2 is a schematic perspective view of an exemplary embodiment of a polishing apparatus 200 for polishing a substrate edge 104 and/or notch of the substrate 102 in accordance with the present invention. The polishing apparatus 200 may include a substrate driver 208 (e.g., a servomotor, gear, belt, chain, etc.), which may be mounted on a pedestal 210. A support 212 (e.g., a vacuum chuck) may be coupled (e.g., rigidly) to a shaft (not shown) of the substrate driver 208. The support 212 may support the substrate 102, for example. The substrate driver 208 may rotate the substrate 102, via the support 212, about a center 214 of the substrate 102 or another suitable axis. The substrate driver 208 may be connected to a substrate driver control unit, such as the controller 112 (FIG. 1), for example, which may control the angular displacement, angular velocity, and/or angular acceleration of the substrate 102. The polishing apparatus 200 may further include a polishing arm 216 aligned in the horizontal plane approximately tangential to an edge of the substrate 102 and supported by a frame 218. The frame 218 may be coupled at one end to a polishing head driver 220. In other embodiments, the polishing arm 216 may be aligned differently, for example, vertically or at an angle with respect to the horizontal plane. The polishing arm 216 may include a polishing head section 222 (‘head’). The polishing head 222 may include a polisher 406 (not drawn to scale), and described further below in FIG. 4. The polisher 406 may be wheel or roller-shaped, as shown herein, or the polisher 406 may be relatively or substantially planar in shape, for example. Any other suitable shape may be used. The polisher 406 may be moved toward or away from the substrate 102 by an actuator (e.g., hydraulic actuator, pneumatic actuator, servomotor, etc.) (not shown). Polishing tape 226, may wrap around the polishing head 222, feed guides 402 (not drawn to scale), and tension distributors 408 (not drawn to scale), described further below with respect to FIG. 4, and over the polisher 406, and be tensioned between take-up and supply spools 232, 234, respectively. The take-up and supply spools 232, 234 may be driven by take-up and supply spool drivers 236, 238 (e.g., servomotors), respectively. The spool drivers 236, 238, may be moved continuously or indexed to precisely control the amount of the polishing tape 226 that is advanced over the polisher 406 from, for example, the take-up and supply spools 232, 234, in order to polish the substrate edge 104.

In one or more embodiments, the abrasive component of the polishing tape 226 may be made from many different materials, such as diamond, aluminum oxide, silicon oxide, silicon carbide, etc. Other materials may also be used. In some embodiments, abrasives used may range, for example, from about 0.1 microns up to about 10 microns in size or, for example, 0.5 microns to 3 microns in size, although other sizes may be used. Different widths of polishing tape 226 ranging from about 0.2 inches to about 1.5 inches may be used, although other polishing tape widths may be used. In one or more embodiments, the polishing tape 226 may be about 0.002 to about 0.02 inches thick and withstand about 1 to 5 lbs. in tension. Other polishing tapes having different thicknesses and tensile strengths may be used. The take-up and supply spools 232, 234 may have a diameter of approximately 10 inches and be capable of holding about 35,000 inches of polishing tape 226, or may have a diameter of approximately 4 inches and be capable of holding about 5,000 inches of polishing tape 226. Other spool dimensions may be used. The take-up and supply spools 232, 234 may be constructed from materials such as nylon, polyurethane, polyvinyl difluoride (PVDF), etc. Other materials may also be used.

Turning to FIG. 3A and 3B, a perspective and schematic perspective view of an exemplary polishing head 300 is provided. As shown in FIG. 3A, the polishing head 300 may include two pairs of feed guides 302 adapted to align/guide and feed a polishing tape 304 through the polishing head 300. The polishing tape 304 may also be advanced over a polisher 306, adapted to press the polishing tape 304 against the substrate 102. Typically, while the feed guides 302 rotate, their location with respect to the polishing head 300 is stationary, and the location of the polisher 306 may move relative to the polishing head 300 to polish the substrate 102. While the feed guides 302 and polisher 306 shown herein are rollers, any suitable shape may be used.

As shown in FIG. 3B, as the polisher 306 presses the polishing tape 304 against the substrate 102, the polisher 306 exerts a force P against the substrate 102. At the same time, the polishing tape 304 exerts a tension force T, having a component that opposes the force P. In some embodiments, for example, the tension force T may be due to the polishing tape 304 being tensioned between supply and take-up spools (not shown), and the position of the feed guides 302 with respect to the polisher 306. As an angle 308 between the polishing tape 304, due to the feed guide 302 position, and a tangent 310 to the contact position of the polisher 306 and the substrate 102 increases from 0 to 90 degrees, for example, the tension force T that opposes the force P increases. When the angle 308 is 90 degrees (herein, pointing to the bottom of the page), for example, the tension force T of the polishing tape 304 directly opposes the force P of the polisher 306 toward the substrate 102. Additionally, when the angle 308 is 90 degrees, the total tension force directly opposing the force P is 2T, as a result of the tension force from both the supply and take-up spools, for example. With the exemplary polishing head 300 shown herein, the angle 308 between the polishing tape 304 and a tangent to the substrate 102 is typically between about 65-70 degrees. As described above, the tension force T varies during the polishing process. The variation may result, for example, from the position of the polishing head 300 and the amount of polishing tape 304 on the take-up and/or supply spools, for example. The variation may make it more difficult to apply a constant force P against the substrate 102 by the polisher 306. For example, if a processing recipe calls for 5 lbs. of force P to be applied by the polisher 306 against the substrate 102, more than 5 lbs. of force, for example 6-7 lbs. of force, may need to be applied to the polisher 306 to account for the tension force T. If the tension force T is changing during the recipe, then the amount of force applied to the polisher 306 to achieve the 5 lbs. of force must be changed as well. The present invention provides apparatus and methods to minimize the effects of the tension force T on the force P exerted by the polisher 306 against the substrate 102.

Turning to FIGS. 4A and 4B, a perspective and schematic view of an exemplary embodiment of a polishing head 400 according to the present invention are provided. The polishing head 400 may include a plurality of feed guides 402. While the feed guides 402 may rotate about a central axis, in some embodiments, the location of the feed guides 402 with respect to the polishing head 400 may be stationary. As shown herein the polishing head 400 includes two pairs of feed guides 402. Any suitable number may be used. Additionally, the feed guides 402 shown herein are rollers, but any suitably shaped feed guide may be used. The polishing head 400 may also include a polishing unit 404. The polishing unit 404 may include a polisher 406 and at least one pair of tension distributors 408. While the tension distributors 408 are shown, and hereinafter referred to, as rollers, any suitably shaped tension distributor 408 may be used. As described below, the tension rollers 408 may be adapted to reduce the amount of tension force T on the polishing unit 404, and the polisher 406 which is a part thereof, and therefore reduce the amount of tension force T affecting the force P exerted by the polisher 406 and/or the polishing unit 404 against the substrate 102. Other suitable amounts of polishers and tension rollers may be used. The tension rollers 408 may be made of PEEK, hard urethane, nylon, or any other suitable material that provides limited particle generation. In some embodiments, the polishing unit 404 may move relative to the polishing head 400, to contact and polish the substrate 102. In other embodiments, the polishing unit 404 may be stationary with respect to the polishing head 400.

As shown in FIGS. 4A and 4B, the polishing tape 226 is routed from the supply spool 234 (FIG. 2), (and in some embodiments over additional guide rollers) through one pair of feed guides 402, then around one of the tension rollers 408, over the polisher 406, then around the second tension roller 408 and finally through the second pair of feed guides 402, before being routed to the take-up spool 232 (FIG. 2), (and in some embodiments over additional guide rollers before being routed to the take-up spool 232). As shown in FIG. 4B, the orientation/position of the tension rollers 408 with respect to the polisher 406 may reduce the effect of the tension force T from the polishing tape 226 on the force P applied by the polisher 406/polishing unit 404 to the substrate 102. In other words, the magnitude of the tension force T may not change, but instead the direction of the tension force T may be changed so that the tension force T may be distributed to both the polisher 406 and the tension rollers 408, thereby reducing the effect of the tension force T on the polisher 406 as compared with the exemplary apparatus 300 of FIGS. 3A and 3B.

In FIG. 4B, the solid lines illustrate the polishing tape 226 and polishing unit 404 in a “balanced” position, wherein an angle 410 between the feed guides 402 and the tension rollers 408 is substantially zero. In this balanced position, the polishing tape 226 may lie horizontally, or in-line, between the feed guides 402 and the tension rollers 408 during polishing. In the balanced position, the two tension forces T, may directly oppose each other, and treating the polisher 406 and tension rollers 408 as a unit, the force P may be applied to the substrate 102 without being affected by the tension force T from the polishing tape 226. In other words, when the two tension forces T directly oppose each other, there may be no substantial net counteracting force on the force P. As the angle 410 is reduced or approaches zero, there is less of an effect of the tension force T on the force P. In some embodiments, the balanced position may be maintained during the polishing process by moving/pivoting the entire head 400 about the substrate 102.

However, in some embodiments, during the polishing process instead of moving the entire polishing head 400 about the substrate 102, the polishing head 400 is maintained a pre-defined distance, such as 1 mm, for example, from the substrate 102, and the polishing unit 404 may pivot/move/extend/retract to contact and polish the substrate 102, as indicated by the dotted lines. The angle 410 may change as the polishing unit 404 moves to polish the substrate 102. As the polishing unit 404 moves from the balanced position, the angle 410 may increase from zero degrees, for example, and thus the net tension force T may increase and have a greater affect on the force P, as the tension force T has a component that opposes the force P. In some embodiments, the angle 410 may vary in a range of about 0 to about 4 degrees, for example. In this range, the force P may be affected very little by the tension force T. Other suitable ranges may be used. Additionally, because the angle 410 may vary in a smaller range than in the exemplary apparatus 300 shown in FIGS. 3A and 3B, the range of compensatory forces applied to the polishing unit 404 to achieve a desired force P may be less, thereby making the force P applied to the substrate 102 easier to control.

For example, in the exemplary apparatus 300 shown in FIGS. 3A and 3B, while a force of 6-7 lbs. may need to be applied to the polisher 306 to achieve a force P of 5 lbs. on the substrate 102, with the present invention, a force of substantially 5 lbs. may be applied to the polishing unit 404 to achieve a force P of 5 lbs. on the substrate 102. In some embodiments, the tension force T may range from a half pound to 5 pounds, and the force P may range from substantially a half pound to 5 pounds. Other suitable tension and polishing unit forces may be used. It should be noted that in some embodiments substantially 5 pounds of force P may be used to achieve optimal polishing.

Turning to FIG. 5, a close-up schematic plan view of the polishing head 400 shown in FIG. 4A is provided. The inventive tension rollers 408 may be coupled to the polishing unit 404 with one or more fasteners, such as screws 500 or other fasteners, for example, which may be adapted to lock the pins (not shown) inserted in the tension rollers 408, for example. The feed guides 402 and the polisher 406 may be coupled to the polishing unit 404 with one or more washers and snap rings 502, for example. Other suitable coupling mechanisms may be used. In the exemplary apparatus 300 of FIGS. 3A and 3B, a plate 506 (FIG. 3A) secures the feed guides 302 to the polishing head 300. The plate 506 traps the polishing tape 304 within the polishing head 300. Therefore, in the apparatus 300, before routing the tape 304 through the polishing head 300, the plate 506 should be removed, which may be time consuming and therefore costly. The embodiment of FIGS. 2, 4A-6 does not include a plate, and therefore the polishing tape 226 may be routed through the polishing head 400 simply by pushing it between the feed guides, polisher and tension rollers 402, 406, and 408.

Turning to FIG. 6, a pictorial flow diagram providing an exemplary method 600 in accordance with the present invention is provided. As described above, the polishing head 400 may be adapted to be oscillated or pivoted/moved (e.g., angularly translated about a tangential axis of the substrate 102 and/or circumferentially relative to the substrate 102) around or along the substrate edge 104 and/or notch so as to polish different portions of the substrate 102. As shown herein, zero degrees is set at the substrate edge 104. Other suitable positions may be set as zero degrees. Additionally, a recipe may determine the length of time the polishing head 400 polishes the substrate 102, such as the edge 104 and notch, at each position. Additionally, or alternatively, a polishing end point may be determined by an amount of film removed from the substrate 102, or the achievement of a particular film profile, for example, as may be detected by sensors (not shown), for example. The recipe may have the polishing head 400 positioned at −90 degrees to begin polishing. In this position, the polishing head 400 may polish a backside of the substrate 102, for example. The polishing head 400 may then pivot such that the polishing head 400 is at a −45 degree angle, as indicated by the directional arrow. In this position, the polishing head 400 may polish a bottom bevel of the substrate 102, for example. Then the polishing head 400 may pivot such that the polishing head 400 is at a 0 degree angle, as indicated by the directional arrow. In this position, the polishing head 400 may polish an outer edge of the substrate edge 104, for example. The polishing head 400 may then pivot such that the polishing head 400 is at a 45 degree angle, as indicated by the directional arrow. In this position, the polishing head 400 may polish an upper bevel of the substrate edge, for example. The polishing head 400 may then pivot such that the polishing head 400 is at a 90 degree angle, as indicated by the directional arrow. In this position, the polishing head 400 may polish an upper surface of the substrate 102, such as an edge exclusion zone, for example. The polishing head 400 may be oriented or positioned at other suitable angles.

Turning to FIG. 7, an exemplary method 700 for polishing a substrate in accordance with an embodiment of the present invention is provided. In step S702, the substrate 102 rotates. The substrate rotation may be controlled by the controller 112, for example. In step S704, the polishing film 226 may contact the substrate 102. As described above, the polishing head 400 may press the polishing film 226 against the substrate 102 with a pre-set force P, in step S706. The pre-set force P may take the opposing tension force T into consideration. In some embodiments, the polishing head and unit 400, 404 may be positioned such that the polisher 406 and tension rollers 408 provide for a zero or substantially zero net effect of the tension force T, while in other embodiments, the polishing head and/or unit 400, 404 may be positioned such that the net effect of the tension force T is reduced, minimized and/or controlled. In step S708, the polishing head 400 pivots about the edge of the substrate 102. As described above, in some embodiments, the polishing head 400 may remain in a relatively fixed position, while the polishing unit 404 pivots about the edge 104 of the substrate 102. When the polishing head 400 remains in a relatively fixed position while the polishing unit 404 pivots about the substrate edge 104, the affects of the tension force T on the force P may be reduced and/or minimized compared to the affects of the tension force T on the force P in the exemplary apparatus 300 shown in FIGS. 3A and 3B. The polishing head 400 may continue polishing the substrate until a specified end point is reached.

The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art.

Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims. 

1. An apparatus comprising: a polishing head, adapted to contact a substrate, wherein the polishing head includes: a polishing unit comprising a polisher and at least one pair of tension distributors positioned to reduce tension on the polisher; and one or more pairs of feed guides.
 2. The apparatus of claim 1 wherein the polishing head is adapted to pivot about an edge of the substrate.
 3. The apparatus of claim 2 wherein the polishing head is adapted to maintain a balanced position while the polishing head pivots about the edge of the substrate.
 4. The apparatus of claim 3 wherein the balanced position provides for an angle between the feed guides and the tension distributors to be substantially zero.
 5. The apparatus of claim 1 wherein the polishing unit is adapted to pivot about an edge of the substrate, and the polishing head is adapted to maintain a fixed position relative to the polishing unit as the polishing unit pivots about the substrate edge.
 6. The apparatus of claim 1 wherein the polisher is adapted to press a polishing tape against the substrate.
 7. The apparatus of claim 6 wherein the polishing head includes two pairs of feed guides.
 8. The apparatus of claim 7 wherein the feed guides are in a stationary location with respect to the polishing head.
 9. The apparatus of claim 7 wherein the polishing tape is routed through a first pair of feed guides, through the polishing unit and then a second pair of feed guides.
 10. The apparatus of claim 9 wherein the polishing unit and first and second pairs of feed guides are adapted to receive the polishing tape while remaining coupled to the polishing head.
 11. The apparatus of claim 1 wherein the polisher, tension distributors and feed guides are adapted to rotate.
 12. The apparatus of claim 1 further comprising a plurality of fasteners adapted to couple the tension distributors to the polishing unit.
 13. A system comprising: a substrate support adapted to rotate a substrate; a polishing head, adapted to contact a substrate, wherein the polishing head comprises: a polishing unit comprising a polisher and at least one pair of tension distributors adapted to reduce tension on the polisher, and one or more pairs of feed guides; and a controller adapted to operate the polishing head.
 14. The system of claim 13 wherein the controller is adapted to move the polishing head into a balanced position relative to an edge of a substrate.
 15. The system of claim 14 wherein the balanced position provides for an angle between the feed guides and the tension distributors to be substantially zero.
 16. The system of claim 14 wherein the controller is adapted to move the polishing unit relative to the polishing head.
 17. The system of claim 13 wherein the polisher is adapted to press a polishing tape against the substrate.
 18. The system of claim 17 wherein the polishing head includes two pairs of feed guides.
 19. The system of claim 18 wherein the polishing tape is routed through a first pair of feed guides, through the polishing unit and then a second pair of feed guides.
 20. A method comprising: rotating a substrate; selecting a balanced position for a polishing head; contacting the substrate with a polishing film, whereby the polishing film is routed through the polishing head; applying a force to the substrate via the polishing film; and pivoting the polishing head about the substrate.
 21. The method of claim 20 wherein the polishing head comprises: a polishing unit comprising a polisher and at least one pair of tension distributors adapted to reduce tension on the polisher.
 22. The method of claim 21 wherein the polishing head further comprises: one or more pairs feed guides.
 23. The method of claim 22 further comprising: pivoting the polishing unit about an edge of the substrate.
 24. The method of claim 23 further comprising: maintaining a fixed position of the polishing head relative to the polishing unit as the polishing unit pivots about the edge of the substrate. 